There are numerous situations where it is important to control light energy and light transmission. For example, in a xerographic reproduction system, such as used in a printer, copier or facsimile machine, light from a source must be modulated into a series of dots (on and off conditions of the light) to form the image which is to be reproduced. The actual reproduction to the final media (typically paper) is accomplished by a rotating drum, or belt, onto which the modulated light dots have been transmitted. The drum is electrostatically charged at the place where the light dots have touched the drum so that ink particles, called toner, adhere to the drum at those places. This toner is then transferred to the paper to create the reproduced image.
In one system, it is desired to begin the process with an ordinary light source such as, for example, a tungsten halogen light bulb, and to reflect the unmodulated light rays from the light source off of a monolithic substrate which has built into it the ability to selectively reflect the light at particular locations on the chip. More specifically, the chip has on it at least one row of small deflectable mirrors which, when undeflected, reflect the light from the light source away from the drum. However, deflection of any, or all, of the individual mirrors causes the deflected mirror to reflect the light from that mirror location onto the drum. At any one time, then, a group of deflections will cause an image of dots, called pixels, to be transmitted to the drum and ultimately printed onto the paper.
It goes without saying then that the ability of the system to accurately capture the proper reflected light and to reject all extraneous other light reflections is critical to the proper performance of the process. However, this is easier said than accomplished since light is particularly difficult to control. Compounding the problem is the fact that the light source must have enough energy to allow for all reflection and transmission losses. While theoretically, it is possible to adjust the undeflected mirrors so that most, if not all, of the nonrequired light is maintained away from the critical path, problems still arise with the substrate itself and with the substrate mounting which reflects light.
One method of light control is to use baffles and light absorbing material. Heat generation, however, can cause warping and other problems if too much light is absorbed by the various elements. Additional problems arise when it is desired to funnel the proper reflected, modulated, light dots to the drum and to mask all other light from the drum. Light absorbing and baffling problems are many faceted, and, if not carefully structured, will require complicated and time consuming manufacturing techniques to achieve.
Since the modulated light must hit the drum in a straight line and since all other light must be shielded from the drum, a system must be established which allows for the controlled disbursement of unwanted light rays while handling the proper modulated light signals. The system is further complicated by the fact that the modulation signals are changing extremely quickly, on the order of approximately 2000 per second, and thus light paths must be closely controlled and extremely repeatable. Because of the close tolerances, light divergences, which come about because of the transmission lengths, must also be controlled. All of these problems must be solved in an economical manner and without complicated alignment and light baffling trial and error techniques.
Thus, there is a further need in the art for such a system which allows for the control of the unwanted light energy without creating excessive heat and without establishing complicated light transmission paths.